Fluid control systems located on earth moving machines, include an operator interface for enabling the operator to control the fluid system, and a hydraulic circuit for controlling the work implements of the machine in response to the operator's inputs. The operator interface may include joysticks adapted to receive the operator inputs and generate the appropriate input signals to control the fluid system. A controller receives the inputs signals and determines the appropriate valve commands. The valve commands are delivered to a valve assembly, or control valve, which controls the fluid flow from a pump to an actuator. In one embodiment, the valve assembly includes a pilot valve and a main valve. An implement of an earth moving machine is connected to one or more actuators. In addition, the pump is driven by a pump engine.
The controller determines a valve command, in response to the operator input signal, and associated hydraulic circuit signals such as the signal received from an engine speed sensor. The valve command signal is then delivered to the appropriate valve assembly. In one embodiment, the valve command signal is delivered to the solenoid of the pilot valve located within the valve assembly. The solenoid is then energized, and controls the valve spool within the pilot valve, to achieve an appropriate position in response to the valve command signal. The pilot valve, then responsively delivers a pilot pressure to the main valve in order to move the main valve, or the spool within the main valve, to the desired position. The main valve then enables fluid to be delivered to the actuator.
In a fluid control system there is a deadband associated with the movement of the joystick from a neutral position, to a position where an initial movement of the actuator being controlled occurs. This deadband may be referred to as a first motion deadband. The deadband may be associated, in part, with the change in valve position needed in order to provide an appropriate amount of fluid flow to the actuator in order to get the actuator to move.
The responsiveness of the actuator is dependent, in part, on the fluid pressure, and fluid flow rate delivered to the actuator. The fluid pressure and fluid rate are in turn dependent, in part, on the main valve position, engine speed, and pump displacement.
The first motion deadband is due, in part, to the amount the main valve needs to move before the main valve enables the appropriate fluid to flow to the actuator. This deadband, between the initial position of the joystick and the position of the joystick where the initial movement of the actuator occurs, is consistent for a given engine speed, pump displacement, and load. However, if the pump engine speed is reduced, for example from a high idle to a low idle speed, then the same joystick command at the high idle speed will not cause the same response of the actuator at the low idle speed. Therefore, the joystick command will need to be increased, for example, as the engine speed is reduced, in order to provide enough fluid flow to the actuator to achieve the same actuator response as in the high idle condition.
Therefore, the first motion deadband varies, in part, on the engine speed and pump displacement of the hydraulic circuit. Variations in first motion deadband result is an inconsistent operator interface which reduces the efficiency of the operator and may lead to errors in the operation of the machine.
The present invention is directed to overcoming one or more of the problems identified above.